Coastal Engineering Projects Research Articles

An engineering approach to wave propagation

Wave propagation is a major topic in most coastal engineering projects. In this paper a new system of equations governing wave propagation is proposed along with a numerical model to solve them. The main intention throughout their derivation was to set the basis for a new engineering tool. Thanks to the ray–front coordinate system, the equations lend themselves to a convenient numerical treatment, which has resulted in practical advantages with respect to parabolic models—the most widespread in coastal engineering practice. Their major limitation is overcome while keeping the computational cost low, as the model proposed in this work allows unrestricted variation of the propagation direction. The problems associated with ray intersections or caustics in conventional ray models are not encountered, as both refraction and diffraction (rather than solely refraction) are considered. After validation through comparison with analytical solutions and physical models, the model utility has been proven by solving engineering cases to which a parabolic model would not be applicable.

Distribution of moisture contents and thermoluminescence ages in an inner shelf borehole from the new Hong Kong International Airport site, China

Offshore boreholes and excavations available through coastal engineering projects in the siliciclastics-dominated inner shelf of the northern South China Sea off Hong Kong have permitted the reconstruction of Quaternary sea-level history dating back to almost 0.5 Ma. In this study, moisture content and thermoluminescence (TL) dating are utilized to help verify ages for marine and terrestrial sediments in a 39.52 m offshore borehole from the new Hong Kong International Airport site. The distribution of moisture contents in borehole samples indicated the presence of three palaeo-desiccated crusts formed by soil development when the marine deposits of Oxygen Isotope (OI) stage 5, OI stage 7 and OI stage 9 were sub-aerially exposed during the low sea-level stand(s) of OI stages 2–4, OI stage 6 and OI stage 8, respectively. Out of the six TL dated borehole samples, three from a terrestrial deposit horizon have yielded finite ages of about 250,000 yr BP suggestive of OI stage 8. In these samples, the TL signal of quartz grains was found to increase well beyond the 250 Gy saturation level with the relatively high radiation fluxes allowing for age determination for only three samples. The three remaining samples of pre-Holocene marine deposits yielded minimum ages each having reached TL saturation. The importance of the moisture content upon the final determination of these sediment ages and the collection and storage of samples for TL dating is clearly demonstrated.

Morphological changes of the Haringvliet estuary after closure in 1970

The Haringvliet estuary is part of the Dutch Delta coast. Since 1950, several large coastal engineering projects have been carried out in the Haringvliet area. The most important of these is the closure of the estuary by the construction of a dam with sluices (finished in 1970). Land reclamation projects of the Maasvlakte (1964–1976) and the so-called Slufter (1986–1987) have also been carried out. These projects have profoundly affected the hydrodynamics and therefore the morphology of the area. New interventions are under discussion and to be able to predict their impact on the morphology, it is necessary to understand the morphological developments caused by the past interventions. In this study, the development with time of the sand volume in the Haringvliet estuary after closure has been studied using bathymetric measurements of the years 1970, 1972, 1979, 1980, 1986 and 1990 until 1999. The changes in sand volume above NAP (Dutch Ordnance Level) −10 m relative to 1970 have been determined. The area in which these volumes have been calculated had to be chosen very carefully to diminish the effects of all other human interventions. As was expected, the estuary shows sedimentation. It could be concluded that the adaptation time scale is about 11 years and that the equilibrium volume has almost been reached in the year 2000.

The interaction between shellfish culture and ecosystem processes

The carrying capacity of the Oosterschelde ecosystem for the production of mussels (Mytilus edulis) was evaluated before and after completion of a large-scale coastal engineering project in 1987. This project caused hydrodynamic and water-quality changes; hence, phytoplankton-species composition changed and phytoplankton turnover increased, but primary production remained the same. In the prebarrier period (1980–1986), condition of mussels showed a significant negative correlation with the annual shellfish standing stock and a significant positive correlation with the annual primary production. The system was exploited at maximum capacity. In the postbarrier period (1987–1997), the significant correlation between mussel condition and primary production remained, but there was no longer a negative correlation between standing stock and condition. This indicates overstocking, but yields were maintained. This was explained by (i) feedbacks of the mussels in the Oosterschelde ecosystem—through their large filtration and nitrogen-regeneration capacity, increased phytoplankton turnover was induced; and (ii) adaptation to the new conditions by the shellfish farmers in their management of the mussel stocks. It was concluded that feedbacks by filter feeders and farmers have to be addressed in estimating the exploitation capacity of ecosystems.

The interaction between shellfish culture and ecosystem processes

The carrying capacity of the Oosterschelde ecosystem for the production of mussels (Mytilus edulis) was evaluated before and after completion of a large-scale coastal engineering project in 1987. This project caused hydrodynamic and water-quality changes; hence, phytoplankton-species composition changed and phytoplankton turnover increased, but primary production remained the same. In the prebarrier period (1980–1986), condition of mussels showed a significant negative correlation with the annual shellfish standing stock and a significant positive correlation with the annual primary production. The system was exploited at maximum capacity. In the postbarrier period (1987–1997), the significant correlation between mussel condition and primary production remained, but there was no longer a negative correlation between standing stock and condition. This indicates overstocking, but yields were maintained. This was explained by (i) feedbacks of the mussels in the Oosterschelde ecosystem—through their large filtration and nitrogen-regeneration capacity, increased phytoplankton turnover was induced; and (ii) adaptation to the new conditions by the shellfish farmers in their management of the mussel stocks. It was concluded that feedbacks by filter feeders and farmers have to be addressed in estimating the exploitation capacity of ecosystems.

Sea level rise shown to drive coastal erosion

Our research has shown that an important relationship exists between sea level rise and sandy beach erosion. The link is highly multiplicative, with the long‐term shoreline retreat rate averaging about 150 times that of sea level rise. For example, a sustained rise of 10 cm in sea level could result in 15 m of shoreline erosion. Such an amount is more than an order of magnitude greater than would be expected from a simple response to sea level rise through inundation of the shoreline.Sea level is certainly only one of many factors causing long‐term beach change. Shoreline revisions from inlet dynamics and coastal engineering projects are more pronounced in most areas of the US. east coast and tend to mask the effect of a rise in sea level even over extended intervals. The implication is that sea level rise is a secondary but inexorable cause of beach erosion in such areas.

Erosion of mud/sand mixtures

The prediction of sediment erosion is an important issue in coastal engineering projects. There are methods for predicting the erosion of cohesive sediment (mud) and non-cohesive sediment (sand), but there are presently no relationships for mixed sediments. However, natural sediments rarely consist of only mud or sand and the erosional properties of combined mud and sand sediments are required so that the whole spectrum of natural sediment size combinations can be modelled. This paper attempts to characterise the erosion behaviour of mixed sediments in a way that can be used for predictive models. In this paper mud (or fines) is defined as clays and silts, which pass through a sieve of size 62.5 μm, and sand is defined as the fraction retained. The collaboration between European researchers in the framework of the MAST G8M project has resulted in the accumulation of an extensive amount of data on the erosion of mud/sand mixtures. The data, which originate from both laboratory and field experiments, has been used to examine the physical processes behind the erosion behaviour of mud/sand mixtures. It was found that adding sand to mud, or vice versa, increases the erosion resistance and reduces the erosion rates when the critical shear stress for erosion is exceeded. The highest values for the erosion shear stress of homogeneously mixed beds occurs at a maximum in the region 30 to 50% sand by weight. The most significant effect on erosion resistance occurs on the addition small percentages of mud by weight to sand. The mode of erosion also changes from cohesionless to cohesive behaviour at low mud contents added to sand, with a transition occurring in the region 3% to 15% mud by weight. The erosional properties are also strongly dependent on the history of the bed and it is common that mud and sand segregate under typical deposition conditions owing to their different settling velocities in water which creates discrete layers. The erosion of these segregated beds should thus be modelled as a sequence of mud and sand erosion “events”.

Geology of the Wrightsville Beach, North Carolina shoreface: Implications for the concept of shoreface profile of equilibrium

Nearly 300 km of 3.5 kHz subbottom profile and 100 kHz sidescan-sonar data, a suite of over 100 short (~2 m) percussion cores and vibracores have been collected on the shoreface and inner continental shelf off Wrightsville Beach, North Carolina. Sidescan-sonar images were analyzed for acoustic backscatter to delineate the surface sediment distribution. Groundtruth data for the sidescan-sonar interpretations were provided by surface grab samples.Cross-shore sediment transport by combined waves and currents is the predominant sedimentologic signature on this shoreface. The shoreface is dominated by a shore-normal system of rippled scour depressions that begin in 3–4 m water depth and extend to the base of the shoreface about 1 km offshore, at 10 m depth. The depressions are 40–100 m wide, and up to 1 m deep. They are floored by coarse, rippled shell hash and gravel; some are separated by rock-underlain fine sand ridges. On the inner shelf, the bathymetric and sedimentary fabrics become shore-oblique, due to a series of relict ridges with 1–2 m of relief. The ridges are coarse on their landward sides and covered on their seaward flanks by thin veneers of fine sand.Field evidence from the Wrightsville Beach shoreface demonstrates that a shoreface equilibrium profile as defined by Dean (1991) and others does not exist here. For example: (1) the grain size varies widely and inconsistently over the profile; (2) shoreface profile shape is controlled predominantly by underlying geology, including Tertiary limestone outcrops and Oligocene silts; and (3) sediment transport patterns cannot be explained by simple diffusion due to wave energy gradients, and that transport occurs seaward of the assumed engineering “closure depth” of 8.5 m. This has several implications for the application of equilibrium profile-based numerical models used to investigate coastal processes and design coastal engineering projects at Wrightsville Beach. The most important practical implication is that a number of assumptions required by existing analytical and numerical models (e.g., Dean, 1991; genesis; sbeach) used for the design of shore protection projects and large-scale coastal modeling over decadal time scales cannot be met.

Cost Implications of Dealing with Environmental Issues in River and Coastal Engineering Schemes

ABSTRACTThis paper identifies those stages of river and coastal engineering projects where expenditure on environmental issues might be necessary. It reviews the types of measures which may be appropriate and, using case studies, provides an order‐of‐magnitude indication of the costs (and benefits) of accommodating environmental needs.

Effect of sedimentological and hydrodynamical changes in the intertidal areas of the Oosterschelde estuary (SW Netherlands) on distribution, density and biomass of five common macrobenthic species: Spio martinensis (Mesnil), Hydrobia ulvae (Pennant), Arenicola marina (L.), Scoloplos armiger (Muller) and Bathyporeia sp.

In order to evaluate the impact of the construction of the storm-surge barrier and secondary dams on macrobenthos of the tidal flats in the Oosterschelde (SW Netherlands), changes in distribution, density and biomass of five common species (Spin martinensis, Hydrobia ulvae, Arenicola marina, Scoloplos armiger and Bathyporeia sp) were analysed. Data on macrobenthos were collected from 1979 to 1989 on five different tidal flats . Changes in sediment texture and hydrodynamic factors during the construction and after the completion of the coastal engineering project were taken into account . Three severe winters in a row caused more disturbance in the population of the main predator of S. armigerthan did the hydrodynamical changes . A temporary prolongation of the emersion time (in 1986 and 1987) caused a temporary decrease in juvenile A. marina.But afterwards they still occupy the same `nursery grounds' . Increased wave action on the edges of the flats probably created new niches for Bathyporeia sp .and Spio martinensis, replacing other benthic species . It is not yet clear what has caused the decline of H. ulvaein many places in the Oosterschelde estuary .

Turbidity, nutrients and phytoplankton primary production in the Oosterschelde (The Netherlands) before, during and after a large-scale coastal engineering project (1980–1990)

Turbidity, nutrients and phytoplankton primary production in the Oosterschelde (The Netherlands) before, during and after a large-scale coastal engineering project (1980–1990)

Mussel culture in a changing environment: the effects of a coastal engineering project on mussel culture (Mytilus edulis L.) in the Oosterschelde estuary (SW Netherlands)

Mussel culture in a changing environment: the effects of a coastal engineering project on mussel culture (Mytilus edulis L.) in the Oosterschelde estuary (SW Netherlands)

Offshore Quaternary sediments and their engineering significance in Hong Kong

Yim, W.W.-S., 1994. Offshore Quaternary sediments and their engineering significance in Hong Kong. In: E.F.J. de Mulder (Editor), Engineering Geology of Quaternary Deposits. Eng. Geol., 37: 31–50. Investigation works undertaken for coastal engineering projects in Hong Kong has provided abundant information on the Quaternary sedimentary sequence beneath the sea floor. Although the significance of such information may not have been realized at the time of these projects, valuable lessons have often been learnt afterwards. Some examples of the important engineering applications concerning offshore Quaternary sediments include: (1) The provision of information on water movement, sediment transport and sedimentation rates during the Holocene period. (2) The identification of exploitable offshore sand and gravel resources. (3) The interpretation of marine geophysical data through the availability of reliable borehole descriptions. (4) The enhancement of engineering soil testing results and their interpretation. (5) The prediction of rates of long-term ground settlement in coastal land reclaimations. (6) The selection of offshore sites for waste disposal. (7) The reduction in cost of coastal engineering projects through choosing the most cost-effective site. (8) The provision of baseline data to assist environmental impact assessment. A new geological model is proposed for the offshore Quaternary sedimentary sequence of Hong Kong. The engineering properties of the sediments are found to be closely related to the palaco-environmental changes.

Nearshore Sediment Transport

Recent advances in understanding of sand movement in the surf zone provide a basis to discuss future directions of research. Problems exist in relating sediment flux and landform responses to waves, tides, and currents despite improved acquisition of data. Some gaps in knowledge are spatial and temporal processes that are geographic. NEARSHORE sediment transport has been a central research theme for coastal scientists. The result has been a dramatic increase in knowledge about surf-zone hydrodynamics. However, additional knowledge is needed to control development of all aspects of beach forms and to determine whether a beach will stabilize, erode, or accrete. Associated with these changes have been environmental regulations and coastal-engineering projects cost- ing more than one billion dollars annually. For most of the shoreline on the globe, data about quantities of sand input, output, and transport are incom- plete, and the relative contributions of longshore and shore-normal transport- beach morphology are unknown for many beaches. Two approaches are now used to predict nearshore sediment transport: (1) bulk transport models that evaluate the total amount of sediment flux in a surf zone based on either wave power or momentum transfer, and (2) instantaneous estimates of dispersal by a bottom shear-stress model that evaluates the fluid force balance at a specific site in a surf zone. Verification and refinement of these models have shifted recently from controlled lab- oratory situations to field experiments, many of which are large and expen- sive, multidisciplinary and interinstitutional such as the Nearshore Transport Study, the Canadian Coastal Sediment Study, and the U.S. Army Corps of Engineers' DUCK experiments. These studies have contributed analytical, empirical, technological, and methodological advances to understanding the dynamics of nearshore transport. The data are still being analyzed, but pre- liminary results indicate that many assumptions in simple models of sedi- ment transport may be inappropriate. Despite these advances, best estimates of nearshore sediment transport are now accurate only to an order of

ARTIFICIAL BEACH UNITS ON LAKE MICHIGAN

High water levels on Lake Michigan during 1985 and 1986 created substantial erosion of the shoreline and reduced the size and recreational potential of many of the parks and beaches. To prevent further erosion, protect existing properties and structures, and to create and improve recreational areas along the Lake Michigan shoreline, four coastal engineering projects were designed and constructed during this time. Artificial beach units stabilized by offshore breakwaters were used as the main component of each project. Physical hydraulic model studies were used to determine the orientation, size, and spacing of breakwaters and artificial beach units. Model predictions of beach profiles and plan shapes compare closely with prototype surveys. Surveys completed since construction demonstrate the stability of the beaches and support their use as effective, low maintenance shoreline protection. Prototype experience has shown that these projects are extremely successful both in their ability to withstand storms on the Great Lakes and to attract people for recreational activities.

Beach morphodynamics along the Nigerian coastline: implications for coastal engineering projects

The morphodynamics states of five Nigerian beaches differing in topographic, tidal and grain size characteristics have been examined as a basis for suggesting the modality for efficient and cost-effective implementation of sand replenishment on eroding beaches. Three of the beaches, namely Forcados, Brass and Ibeno, fluctuated between the dissipative and intermediate morphodynamic states while Badagry and Victoria Beaches varied between reflective and intermediate states. Recent and on-going investigations at Ibeno Beach reveal that reflectivity values approaching those of dissipative state were characterized by low beach mobility and net sediment exchange minimal. On the contrary, a shift towards reflective state with low reflectivity values resulted in high and rapid erosion. The major implication of the above results demands that sand replenishment must be implemented in a manner that will ensure the persistence of dissipative condition. Given the present state of knowledge of wave conditions along the Nigerian coast, dissipative state would be enhanced if sand replenishment does not increase the foreshore and surf zone slope beyond 7°.

Reviews: The Great Australian Nightmare: A Critique of the Home-Ownership Ideology, Rental Housing in the 1980s, Quality of Life and Human Welfare: Proceedings of the Third Royal Scottish Geographical Society Symposium, Urban Inequalities under State Socialism, High Technology Small Firms: Innovation and Regional Development in Britain and the United States, Exploring Social Geography, Cities in the Developing World: Policies for

Reviews: The Great Australian Nightmare: A Critique of the Home-Ownership Ideology, Rental Housing in the 1980s, Quality of Life and Human Welfare: Proceedings of the Third Royal Scottish Geographical Society Symposium, Urban Inequalities under State Socialism, High Technology Small Firms: Innovation and Regional Development in Britain and the United States, Exploring Social Geography, Cities in the Developing World: Policies for

Decision-Making in Coastal Engineering

One of the major objectives of this symposium is to promote the integration of ecological aspects into the decision-making processes associated with coastal engineering projects and the protection and longterm management of the areas around the projects. In the decision-making process we can distinguish: participants, issues, strategies, procedures and interferences in the process. Each of these elements may incorporate environmental aspects in the decision-making process. In case of very large and complex projects special measures will be required, for instance the creation of special committees or boards with adequate political support and legal power.

Environmental Conflicts in a Rapidly Growing Coastal Economy: The Case of South Florida

The coastal areas of South Florida contain hundreds of kilometers of beaches, barrier islands, estuaries and coastal wetlands; they also hold most of the state's major centers of population. As South Florida continues to grow rapidly, numerous environmental problems associated with coastal engineering projects must be addressed. The paper discusses selected states legislation and several notable examples of conflicts between development and the coastal environment: construction on coastal wetlands; water supply requirements of rapid growth; nuclear power plant siting; and protection of beaches and barrier islands. It also considers the need to resolve such conflicts and to balance the requirements of coastal engineering projects with environmental protection.

Appropriate Methods for Tropical Coastal Resource Inventory and Monitoring

Most investments in research, development and management for coastal engineering projects have taken place in temperate zones, usually in areas of highly developed infrastructures. There is a need for more coastal engineering in poor tropical regions, and many contend that the economic status of this part of the world is a consequence of poorly developed infrastructures. The provision of appropriate information on resources and ecology in the tropics, against which coastal engineering projects can be evaluated, requires special techniques for inventory and monitoring. Methods are influenced by the particular biologies of tropical coastal ecosystems, and by the undeveloped state of economies and infrastructures. A selection of methods found suitable for tropical coastal studies in Eastern Africa is described, including remote sensing, multi-stage sampling, non-biased quantification techniques, fixed point monitoring, low-level aerial surveillance and reconnaissance, an aerial collecting drogue, and a matrix analysis for evaluating environmental consequences in valid economic terms.